Test Pipelines for Leaks
How Can One Test Pipelines for Leaks?
Pipes have proved to be a highly efficient way to transfer water for centuries. Today, however, they are used to carry a far wider range of liquids, from corrosive chemicals and vegetable oil to crude oil and liquid petroleum. In addition, they are commonly employed to transfer gases and even solids in liquid suspension, such as coal slurries. Whatever they may be used to carry, they can become damaged and so there is a need to test pipelines for leaks from time to time. In practice, there are a variety of ways in which this can be done.
The simplest, and by far the least reliable of these, is to carry out a direct inspection. In this procedure, one or more workers will travel the length of the pipe using special tools to detect any potential weak spots in their structure. Of course, this method is only suitable for exposed pipes and not for those buried underground while, even above ground, it can frequently fail to reveal damage that is not readily visible to the unaided eye.
A more reliable way to test pipelines for leaks is to perform a hydrostatic examination. To do so involves raising the pressure within the pipe to a level that is considerably higher than its normal operating pressure. The regulations governing the pressure required vary between countries, as does the length of time for which it must be applied for testing purposes, but it is likely to be somewhere between 25 and 50% above normal – and maintained for several hours.
To test pipelines for leaks in this manner, the pipe must first be evacuated and then filled with water to which pressure is then applied by means of specialised pumps. If the pipe is undamaged, the pressure should remain constant throughout the required time period, whereas it will tend to fall if any water is escaping from a crack in the wall of such a pressurised pipe. It must be emphasised that this is not intended to be destructive testing but, nevertheless, it could lead to further weakening of any areas that might be already damaged.
Hydrostatic testing is designed to detect damage from within the pipe and this may also be achieved by visual means. To test pipelines for leaks visually, a remotely controlled, mobile video camera can be inserted into the line and used to record and relay imagery from inside the pipe to observers stationed on the outside. This type of procedure, however, is more suited to the inspection of storm drains and underground sewer systems and is not considered practical for use in industrial pipelines such as those used in oil and gas plants.
Used to locate and identify physical damage rather than to test pipelines for the presence of leaks, the in-line inspection technology, colloquially known as “smart pigging”, employs a cylindrical device known as a “pig” to travel along the pipe and employ various sensors to detect anomalies. It can then record and store data regarding the possible nature of any damage and its precise location within the pipe, which can then be interpreted by a human operator.
For more on how to test pipelines for leaks, chat with an expert at Oleum Process & Pipeline Services.